Ultrasonic welding is typically used to join multiple parts together using vibrations converted into heat energy. Common types of ultrasonic welding are plunge and continuous welding. In plunge welding, an ultrasonic horn plunges (travels towards the parts) and transmits vibrations into a top part. In continuous welding, for example scan or rotary welding, the ultrasonic horn is typically stationary or rotating and the part is moved beneath it. Continuous ultrasonic welding is typically used for sealing fabrics, films, and other parts. Each of the ultrasonic welding types involves a horn.
Ultrasonic horns impart energy to the parts to be welded at a selected wavelength, frequency, and amplitude. The horn resonates at the frequency of the ultrasonic transducer energizing it; transducers having a frequency of about 20,000 Hertz being perhaps the most commonly available commercially. For example, a rotary horn typically includes a shaft with input and output ends, and a welding portion mounted on and coaxial with the output end. The diameter of the welding portion is typically greater than the diameter of the shaft. The welding portion has a cylindrical weld face having a diameter that expands and contracts with the application of vibration energy. Typically, a rotary horn is cylindrical and rotates about a longitudinal axis. The input vibration is in the axial direction and the output vibration is in the radial direction. The horn and anvil are conveniently mounted close to each other, and the anvil can rotate in the opposite direction of the horn. The part (or parts) to be welded passes between the cylindrical surfaces at a linear velocity, equal to the tangential velocity of the cylindrical surfaces.
As might be expected, the fact that the horn is undergoing intense vibration gives rise to the problem of maintaining a grip on it during operation. Typically, two methods are used to mount an ultrasonic horn: nodal mounting and non-nodal mounting. A node is a position of the horn that has zero displacement in one or more directions. As used with respect to horns in this application, a node is a point or region on an ultrasonic horn where the longitudinal displacement is negligible or zero and the radial displacement is at or near its maximum when the horn is in resonance. An anti-node is a point or region where the longitudinal displacement is at or near its maximum and the radial displacement is at or near its minimum.
Co-assigned U.S. Pat. No. 6,786,384, “Ultrasonic Horn Mount,” which is hereby incorporated by reference, discloses an effective mount for a rotary ultrasonic horn having a predetermined resonant frequency. The disclosed mount has itself about the same resonant frequency such that the mount is driven by the horn it is holding in such a way that the radial displacement imparted by the horn to the mount is dissipated such that an outer bearing surface is left largely unmoving (in a radial sense, during operation it is rotating circumferentially).
Unfortunately, this disclosure is unhelpful with regard to mounting a linear horn for scan welding. The art would be advanced by providing the advantages of a resonant, nodal mount to a linear welding horn.